The star architecture of the multiple access communications system consists of a hub station in the center of the star and remote stations of which there is one each at the star. It is assumed that a communications path exists by which the hub station transmits information to each of the remote stations and this path is called the forward link. It is assumed that a communications path exists by which an individual remote station transmits information to the hub station and this path is called the return link. A star architecture with K remote stations is shown in FIG. 1.
The object of this invention is to provide apparatus and method for the synchronization of signal timing in a multiple access communications system.
The present invention is part of that multiple access communications system which is configured in a star architecture and for which it is necessary that all return link signals received at the hub station are time synchronous. All signals possess the same time division multiplex structure in which a portion of the signal is dedicated to a time synchronization burst. This invention specifies that burst sequence for each individual signal and provides a time tracking delay-lock loop for each individual signal even though the sync bursts from all of these received signals are coincident in time and frequency. The novelty of this invention is the use of special sync burst sequences in the well known time-gated delay lock loop (Spilker, J.J. DIGITAL COMMUNICATIONS BY SATELLITE, Englewood Cliffs, N.J., 1977, Prentice-Hall, pp. 555-569). These sync burst sequences are specified so that the interferences between coincident signals is minimized for timing offsets up to .+-.1 chip, which means that the time tracking and synchronization process for each return link is relatively unaffected by all of the others. To implement the time tracking loop a portion of the forward link information capacity is allocated to the signal timing error data which the remote station uses for timing correction. It is assumed that each remote station receives its own timing error data in a robust, uncorrupted manner. A portion of the return link information capacity is allocated to the sync burst which is received by the hub station and processed by the delay discriminator.